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United States Patent |
5,722,417
|
Garbe
|
March 3, 1998
|
Long function monitoring apparatus flowheads
Abstract
Flowheads are described for use in expiratory flow measuring equipment.
They are designed to be disposable and to fit on the casing of a unit
containing a pressure transducer and associated electronics. The pressure
transducer is placed, when the unit is fitted to the casing, in
communication with ports (8 and 9) in the wall of a main tube, which ports
are respectively upstream and downstream of a central perforated wall (5)
which constitutes a passage restriction and across which a pressure drop
is accordingly generated if breath is exhaled through the tube. Low
pressure drop hydrophilic filters may be used to damp high frequency
pressure oscillations and to protect the instrument from ingress of
condensed water vapour.
Inventors:
|
Garbe; Bernhardt Rudolph (Green Acres, Thrornborough, Buckinghamshire MK18 2DJ, GB)
|
Appl. No.:
|
672541 |
Filed:
|
June 28, 1996 |
Foreign Application Priority Data
| Jun 30, 1919[GB] | 9513370.8 |
Current U.S. Class: |
600/538; 73/861.52; 600/529 |
Intern'l Class: |
A61B 005/087 |
Field of Search: |
128/716,720,724,725
73/861.52
|
References Cited
U.S. Patent Documents
5060655 | Oct., 1991 | Rudolph | 128/725.
|
5107860 | Apr., 1992 | Malouvire et al.
| |
5357972 | Oct., 1994 | Norlien.
| |
5564432 | Oct., 1996 | Thomson | 128/725.
|
Foreign Patent Documents |
EP 0 627 196 A1 | Dec., 1994 | EP.
| |
Primary Examiner: Bahr; Jennifer
Assistant Examiner: Kearney; Rosiland
Attorney, Agent or Firm: Breiner & Breiner
Claims
I claim:
1. A flowhead for use in lung function monitoring apparatus consisting
essentially of a molded body member; a substantially cylindrical main
channel within the body member; a mesh integrally molded with the body
member, said mesh extending across an entire cross-section of the channel
and dividing the channel transversely into two sections; and axially
spaced ports in a side wall of the body member which are in communication
with the channel, with one port being located on each side of the mesh,
and each port having an axis parallel to one another and transverse to a
longitudinal axis of the channel; wherein each port is surrounded on an
exterior surface of the body member by a cylindrical sealing collar, and
wherein the mesh includes a plurality of narrow substantially cylindrical
passages axially aligned with the longitudinal axis of the channel.
2. A flowhead of claim 1 further including a hydrophilic filter material
covering each port.
Description
FIELD OF THE INVENTION
This invention relates to lung function monitoring apparatus.
BACKGROUND OF THE INVENTION
In various diagnostic and monitoring procedures for people with breathing
difficulties, particularly asthmatics, it is desirable to be able to carry
out checking on a number of physiological parameters. Two of the most
important of these for diagnostic purposes is the peak expiratory flow
i.e. the maximum flow rate at which the person can exhale, and the
FEV.sub.1 (Forced Expiratory Volume at one second), that is the volume
expired in the first second.
Simple mechanically operating peak flow meters have been known for some
time and have acquired widespread popularity. They are inexpensive to
manufacture and can be issued to individual patients for continuous
monitoring, for example checking their peak expiratory flow three times a
day. Devices of this type are described for example in patent
specifications GB 1463814 and WO 91/11140.
For more sophisticated and accurate testing and measurements, spirometers
are available. These generally cost hundreds or thousands of pounds and
are widely used in clinical practice, but they are not suitable for quick
checking, they are not particularly portable, and accordingly not always
convenient for use.
With the advent of modern electronics, it is possible to produce
considerably more compact apparatus which may be used by medical
professionals and even be designed for personal use. UK-A-2238389
describes such apparatus. The apparatus described in that specification,
however, is effectively restricted to personal use by a single user since
it will naturally, even if mouth pieces with filters are used, be subject
to bacterial contamination from the users exhaled breath and thus cannot
be used by another patient without danger and cross infection.
A classic approach to measuring fluid flow is to cause the fluid flow to
pass through a channel containing a constriction and measuring the
pressure in the channel upstream and downstream of the constriction.
Nowadays electronic differential pressure transducers are widely available
and one of these e.g. located at the ends of a pair of lateral channels
one upstream and one downstream of the constriction in the flow passage,
can be connected to suitable circuitry to analyze and display the result.
The present invention is directed to the construction of a channel member
through which the exhaled air is expelled, and which can be produced
inexpensively as a disposable unit which can be easily attached to, and
detached from, a basic electronic measuring unit containing the transducer
and associated circuitry. A particular advantage of the present invention
is that the disposable flowheads may be manufactured in a very consistent
manner so as to have a constant differential pressure across the flowhead
which has the result that the electronic measuring unit does not lose
calibration when the flowhead is changed.
GENERAL DESCRIPTION OF INVENTION
According to the present invention there is provided a flowhead for use in
such apparatus consisting of a body member defining a substantially
cylindrical main channel divided transversely into two sections via a mesh
extending across the entire cross-section of the channel, axially spaced
ports in the side wall of the channel to either side of the mesh, the axis
of each port being transverse to the longitudinal axis of the channel and
parallel the axes of the ports being with one another, and wherein each
port is surrounded on the exterior of the channel by a cylindrical sealing
collar.
The sealing collars are designed to mate with corresponding cylindrical
sleeves or apertures on the casing containing the transducers and
associated electronics, each sleeve or aperture surrounding a passage
leading to a transducer.
The mesh dividing the channel is preferably an integrally moulded mesh
consisting of a series of narrow generally cylindrical passages axially
aligned with the main axis of the channel. Alternatively the mesh may be
inserted into the moulding, the moulding could take place around a
preformed mesh; or the moulding could take place around a piece of
material which is to be machined into a mesh at a later time in the
manufacturing process.
It is highly preferred to incorporate within the passages on either side of
the mesh and covering the lateral ports a hydrophilic filter material,
preferably one based on a non-woven fabric such as those commercially
available under the trade mark FILTRETE. The use of such filter material
assists in damping out high frequency pressure oscillations and according
reducing the possibility of damage to the pressure transducers.
The mesh design not only creates a pressure drop between the two ports of
the channel but is also preferably designed to ensure a consistently
turbulent flow profile across the entire cross-section of the channel.
DESCRIPTION OF PREFERRED EMBODIMENT
The invention is illustrated by way of example with reference to the
accompanying drawings in which:
FIG. 1 is an axial section through a disposable flowhead in accordance with
the invention, and
FIG. 2 is a cross-section along the lines 2--2 in FIG. 1.
Referring to the drawings, the unit consists basically of a main tubular
body 1 having integrally moulded therewith an extending lateral skirt 2
which is adapted to mate with the upper surface of the casing of a unit
containing the pressure transducer and associated evaluation electronics.
Depending from skirt 2 are two integral tabs 3 which may mate and latch
with corresponding formations on the aforesaid casing.
The central substantially tubular passage is divided into two the presence
of a perforate integral wall 5, i.e., a mesh. As can clearly be seen in
FIG. 2, wall 5 is pierced by a plurality of cylindrical passages forming
an array and including six cylindrical passages of slightly smaller
dimensions than the rest in order to fill the entire cross-section
efficiently. The array as shown in FIG. 2 is a particularly preferred
embodiment of the present invention. We have found that this design
provides a flow profile which is consistently turbulent across the range
of expiratory flow for which the unit is designed.
In the wall of body 1 are two small apertures, one denoted 8 upstream of
the wall 5 and the other denoted 9 downstream of it. On the outside of the
main passage, these apertures are each surrounded by a cylindrical skirt
12 and 13 respectively. These skirts 12 and 13 are dimensioned with
slightly tapered walls to mate and seal with corresponding formation on
the casing of the main unit containing the pressure transducers and
associated electronics. When the unit shown in FIGS. 1 and 2 is fitted to
the casing, each of ports 8 and 9 is in respective communication with a
pressure transducer located within the main equipment casing.
The left hand end of the unit as shown in FIG. 1 has a tapered exterior 15
over which may be fitted a suitable mouthpiece. The mouthpiece may be of
conventional type and may if desired incorporate a non return valve
enabling exhaled air to be blown through the flowhead shown in FIG. 1 from
left to right, but not sucked back from right to left.
The flowhead may incorporate a low resistance hydrophilic filter to cover
port 8. This has two advantages: first ther is a major reduction in the
ease with which e.g. airborne moisture droplets could pass through port 8
and into the passage leading from the exterior of the main equipment
casing to the pressure transducer and thereby prevent the water droplets
finding their way into the transducer and thereby preventing proper
operation. Secondly, the provision of such filter material serves to damp
high frequency pressure oscillations which can arise within the main tube,
thus reducing the possibility of any damage to the transducer. A second
filter may be placed over port 9 for similar purposes.
In use, when exhaled breath is blown through the unit from left to right as
shown in FIG. 1, because of the presence of the wall 5 which constitutes a
constriction or resistance to the flow, the pressure upstream of wall 5 at
port 8 is greater than that downstream of it at port 9. This difference is
detected by the pressure transducer and may be converted by using known
algorithms to a corresponding expiratory flow rate and by integration of
the signal to a one second volume of expired air. The electronics may
naturally sample this flow rate during the course of an exhalation and be
arranged to display the peak expiratory flow rate and/or FEV.sub.1 (Forced
Expiratory Volume at one second).
The flowhead in accordance with the invention is preferably manufactured as
an integral moulding from a suitable plastics material. Various
commercially available grades of polystyrene have proved suitable. Care
needs to be taken, however, for efficient reliable and repeatable
operation, to ensure that the moulding around the apertures in wall 5 and
around the two ports 8 and 9 is clean and free of any flash. By careful
mould design, the flowhead may be produced as a disposable item, thus
obviating the need to clean and disinfect the flowhead after use by one
patient and before use by the next.
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